Dry etching method

Abstract

The dry etching method of the present invention is characterized in that: for a laminated film of a silicon oxide layer and a silicon nitride layer formed on a substrate, etching is performed through a mask formed on the laminated film by plasmaizing a dry etchant and applying a bias voltage of 500 V or more, thereby forming a through hole in the vertical direction of the layer. And the dry etchant contains at least an unsaturated perfluorocarbon represented by C3H2F4, C x F y and an oxidizing gas, and the volume of the unsaturated perfluorocarbon contained in the dry etchant is in the range of 0.1 to 10 times the volume of the C3H2F4 contained in the dry etchant. By this dry etching method, the ratio of the etching rate of SiO x to the etching rate of SiN (SiN / SiO x ratio) can be arbitrarily controlled between 0.90 and 1.5, and a high etching selectivity for the mask can also be achieved.

Description

[0001] Relevant information on divisional applications

[0002] This is a divisional application. The parent application of this divisional application is a patent application for invention with the application date of July 1, 2016, application number 201680044981.7, and invention title "Dry Etching Method". Technical Field

[0003] The present invention relates to a dry etching method using a dry etchant containing a fluorinated unsaturated hydrocarbon. Background Art

[0004] Currently, in semiconductor manufacturing, miniaturization is approaching the physical limit. To compensate for this, the industry is developing methods of integrating by stacking structures in the height direction. This tendency is particularly significantly observed in NAND flash memories, and research and development of three-dimensional NAND flash memories are being actively carried out.

[0005] For example, in the three-dimensional NAND flash memory described in Non-Patent Document 1, the following structure is adopted: a polysilicon (hereinafter referred to as poly-Si or p-Si) layer and a silicon oxide (hereinafter referred to as SiO x ) layer are alternately stacked multiple layers on a substrate, and structures serving as electrodes are embedded in the vertical direction in this layer. However, in the case of actually manufacturing such an element, since both the substrate as the base and the layers contained in the stacked film are Si, in the etching step of the stacked film, the substrate is damaged, and it is difficult to etch only the stacked film containing p-Si and SiO x .

[0006] Therefore, as shown in Non-Patent Document 2, NAND flash memories using a stacked film containing silicon nitride (hereinafter referred to as SiN) and SiO x instead of the stacked film containing p-Si and SiO x have also been studied. In an example of the manufacturing method in this case, as shown in Fig. 1(a), an alternating stacked film containing a SiN layer 1 and a SiO x layer 2 is prefabricated on a substrate 4. As shown in Fig. 1(b), a through hole 5 is formed in the vertical direction in this layer by etching. Thereafter, although not shown, steps such as removing the SiN layer to form a gate are also performed.

[0007] In the step of forming a through hole in the vertical direction in the layer of this stacked film, as shown in Non-Patent Document 3, the following step is disclosed: when forming a large-capacity memory called BiCS (Bit Cost Scalable), as separate steps, etching of Si and etching of SiO2 are alternately repeated for an alternating stacked film of Si and SiO2 to form a through hole.

[0008] However, since etching is performed as separate steps for each layer, the number of steps increases significantly as the number of stacked layers increases. In addition, if only the conventional CF-based gas is used, the etching rate of SiN is slow, and deposition may occur on the SiN layer depending on the circumstances, making it impossible to obtain the required etching shape. Therefore, as shown in Patent Document 1, there is also a case of using the following method: etching different types of layers simultaneously using a single plasma etching with a mixed gas containing a CF-based gas and a CHF-based gas.

[0009] In addition, Patent Document 2 discloses that an etchant containing a fluorinated unsaturated hydrocarbon mainly composed of HFO-1234ze(E) has a high etching rate for both SiN and SiO2, and has a high selectivity to the mask, enabling high aspect ratio etching.

[0010] [Prior Art Documents]

[0011] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Laid-Open No. 2003-86568

[0013] [Patent Document 2] Japanese Patent Laid-Open No. 2012-114402

[0014] [Non-Patent Documents]

[0015] [Non-Patent Document 1] Hideaki Aochi, et al., Toshiba Review, September 2011, Vol. 66, No. 9, pp. 16-19

[0016] [Non-Patent Document 2] Jim Handy 'An Alternative Kind of Vertical 3D NAND String', [online]; The Memory Guy, [issued on November 8, 2013], URL <URL: http: / / thememoryguy.com / an-alternative-kind-of-vertical-3d-nand-string / >

[0017] [Non-Patent Document 3] Hisashi Ichikawa, et al., Toshiba Review, May 2011, Vol. 66, No. 5, pp. 29-33 Summary of the Invention

[0018] [Problems to be Solved by the Invention]

[0019] As described above, Patent Document 1 discloses the following method: by using a mixed gas containing a CF-based gas mainly composed of C4F8 and a CHF-based gas containing hydrogen, different types of layers are etched simultaneously using a primary plasma etching. However, there are the following problems in these methods: the etching selectivity with the mask is not sufficiently obtained, and when the film thickness of the laminated film is thick, the mask cannot withstand until the etching is completed. In addition, the formation of the sidewall protective film is also insufficient during this etching process, resulting in problems such as abnormal etching shapes like bowing.

[0020] On the other hand, as disclosed in Patent Document 2, an etchant containing 1,3,3,3-tetrafluoropropene, an additive gas, and an inert gas has a higher etching selectivity for the mask compared to a CF-based gas mainly composed of C4F6 or C4F8, and can suppress abnormal etching shapes such as faceting or bowing of the mask.

[0021] Here, it is also clearly known from the examples of Patent Document 2 that in an etching gas containing 1,3,3,3-tetrafluoropropene, an additive gas, and an inert gas, the etching rate of SiN is about 1.2 times that of SiO x This characteristic is effective in preventing abnormal etching shapes caused by a decrease in the etching rate of the SiN layer when only using the CF-based gas, but for deep etching of a laminated film for forming a through-hole with an extremely large aspect ratio exceeding 20, it may become a new cause of abnormal etching shapes. It is known that the reason is that the inventors et al. applied a relatively large power and ion energy in order to obtain sufficient etching rate and ion linearity, and as a result, the decomposition of the etching gas proceeded excessively, or the etching of the SiN layer became too large compared to the etching of the SiO x layer, and this ratio reached more than 2.0 times at most, causing isotropic etching of the SiN layer to occur in addition to anisotropic etching.

[0022] It is known that the Si-N bond constituting SiN has a weaker bond energy compared to the Si-O bond constituting SiO x Therefore, if SiO x is not in a state where the ion energy is increased by applying a bias voltage, etching hardly proceeds. On the other hand, SiN is relatively easily etched even without applying a bias voltage when using an etching gas containing H atoms and F atoms for etching. Therefore, it is considered that when performing the etching with the high aspect ratio, SiN is selectively etched isotropically also in the horizontal direction. In addition, structurally, there is a case where a SiN layer exists on the SiO x layer. In this case, compared to the SiO xInstead of the etching rate, the etching rate of SiN in the horizontal direction of this layer becomes larger. As a result, as shown in Figure 2 , excessive SiN etching in the horizontal direction of the SiN layer occurs.

[0023] The mechanism of the excessive generation of this horizontal SiN etching is explored as follows. In a normal etching process, there are always active substances with a potential that can perform both anisotropic etching and isotropic etching on SiN in the holes. Adding ions accelerated by a bias voltage here makes anisotropic etching, in addition to isotropic etching, also dominant. However, it is generally believed that when the underlying SiO x layer is exposed, since there is no SiN in the vertical direction with respect to this layer, the active substances for SiN do not contribute to the anisotropic etching but contribute to the isotropic etching in all horizontal directions. Therefore, it is considered that the isotropic etching in the horizontal direction of the SiN layer accelerates compared to the case where the underlying SiN layer is exposed through the SiO x layer.

[0024] In the case of excessive etching in the horizontal direction of the SiN layer, unexpected voids are formed in the stacked structure, leading to the collapse of the structure. Therefore, it is necessary to reduce the ratio of the etching rate of SiO x to the etching rate of SiN (SiN / SiO x ratio) to suppress the excessive etching in the horizontal direction of the SiN layer. Specifically, a dry etching method is expected to arbitrarily control the ratio of the etching rate of SiO x to the etching rate of SiN (SiN / SiO x ratio) between 0.90 and 1.5.

[0025] Although Patent Document 2 discloses a method of selectively etching SiN or SiO x , the specific method of arbitrarily controlling the etching rates of SiN and SiO x has not been disclosed.

[0026] The present invention has been completed in view of the above problems, and its object is to provide an etching method that uses 1,3,3,3-tetrafluoropropene as an etching gas for plasma etching, and for a stacked film of SiO x and SiN, can arbitrarily control the ratio of the etching rate of SiO x to the etching rate of SiN (SiN / SiO x ratio) between 0.90 and 1.5, and also has high selectivity for the mask.

[0027] [Technical means for solving the problem]

[0028] The present inventors have conducted various studies to achieve the above-mentioned purpose and have found that: x In the step of forming a through hole perpendicular to the layers at a portion where multiple layers are alternately stacked on a substrate, plasma etching is performed using a dry etchant containing at least 1,3,3,3-tetrafluoropropylene and an unsaturated perfluorocarbon having 2 to 5 carbon atoms at a specific ratio, thereby etching the SiO x The ratio of the etching rate of SiN to the etching rate of SiN (SiN / SiO x The ratio) is arbitrarily controlled to be between 0.90 and less than 1.5, and the etching selectivity to the mask is also high, thereby completing the present invention.

[0029] That is, the present invention provides a dry etching method, characterized in that: a laminated film of a silicon oxide layer and a silicon nitride layer formed on a substrate is etched by plasma-forming a dry etchant and applying a bias voltage of 500V or more through a mask having a specific opening pattern formed on the laminated film, thereby forming a through hole in a vertical direction in the layer, and the dry etchant contains at least C3H2F4, C x F y An unsaturated perfluorocarbon and an oxidizing gas represented by (x=an integer from 2 to 5, y=2, 4, 6, 8 or 10, y≦2x), and the volume of the unsaturated perfluorocarbon contained in the dry etchant is in the range of 0.1 to 10 times the volume of the C3H2F4 contained in the dry etchant.

[0030] The unsaturated perfluorocarbon is at least one selected from the group consisting of C3F6, C4F6, C4F8 and C5F8, and the total concentration of the unsaturated perfluorocarbon and C3H2F4 in the dry etchant is preferably 5 volume % or more.

[0031] In addition, the dry etchant may also only contain C3H2F4, the unsaturated perfluorocarbon, the oxidizing gas and the inert gas.

[0032] In addition, it is preferred that C3H2F4 is 1,3,3,3-tetrafluoropropylene.

[0033] According to the present invention, in the manufacturing process of a three-dimensional NAND flash memory, SiN and SiO are connected. x In the step of forming a through hole perpendicular to the layer at a location where multiple layers are alternately stacked on the substrate, SiO x The etching rate of SiN is relative to the etching rate of SiN (SiN / SiO xThe ratio (aspect ratio) can be arbitrarily controlled to be between 0.90 and less than 1.5, and the etching can also be highly selective to the mask. As a result, excessive isotropic etching of the SiN layer exposed in the through hole formed in the laminated film can be suppressed, and collapse of the laminated structure during etching of the through hole with an aspect ratio exceeding 20 can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1( a ) and ( b ) are schematic diagrams of the layered structure of the element before and after the through-hole is formed.

[0035] Figure 2 This is a schematic diagram of unexpected SiN isotropic etching that occurs during etching.

[0036] Figure 3 This is a schematic diagram of a reaction apparatus used in Examples and Comparative Examples.

[0037] Figure 4 (a) and (b) show SiN / SiO x Etching rate ratio and etching selectivity ratio (SiO x / resist) diagram. DETAILED DESCRIPTION

[0038] Hereinafter, the implementation method of the present invention will be described. In addition, the scope of the present invention is not limited to these descriptions, and it is also possible to implement it by making appropriate changes in the range other than the following examples and without damaging the gist of the present invention.

[0039] In the dry etching method of the present invention, as shown in FIG. 1( a), a SiN layer 1 and a SiO layer 2 are pre-made on a substrate 4. x An alternately laminated film of layer 2 and a mask 3 having a specific opening pattern are provided, and as shown in FIG1(b), a through hole 5 is formed by etching in a direction perpendicular to the layer, that is, perpendicular to the substrate 4, through the mask 3. Here, the alternately laminated film is a laminated film formed by laminating 32 layers, 48 ​​layers or more in practicality, so the through hole 5 is a very long and narrow hole with an aspect ratio (a value obtained by dividing the thickness a of the alternately laminated film by the width b of the opening of the mask 3) of 20 or more.

[0040] In the dry etching method of the present invention, plasma etching is performed using the following dry etchant to thereby etch SiO2 formed on a substrate. x The stacked film of the layer and the SiN layer is etched, and the dry etching agent contains at least C3H2F4, C x F yAn unsaturated perfluorocarbon and an oxidizing gas represented by (x is an integer from 2 to 5, y is 2, 4, 6, 8 or 10, and y ≤ 2x), and the mixing ratio of C3H2F4 to the unsaturated perfluorocarbon is in the range of 1:0.1 to 10 by volume. The substrate used is not particularly limited, and a silicon wafer can be used. As the material constituting the mask 3, amorphous carbon can be used.

[0041] As the C x F y The unsaturated perfluorocarbons represented can include compounds selected from the group consisting of C2F2, C2F4, C3F4, C3F6, C4F2, C4F4, C4F6, C4F8, C5F4, C5F6, C5F8, C5F 10 and mixtures thereof. If the amount of F atoms contained in C x F y relative to C atoms is small, there is a tendency for the etching rate of not only the SiN layer but also the SiO x layer to decrease. Therefore, C2F4, C3F6, C4F6, C4F8, C5F8, C5F 10 are preferred. If the ease of operation such as vapor pressure or explosiveness is considered, C3F6, C4F6, C4F8, C5F8 are particularly preferred.

[0042] C x F y The unsaturated perfluorocarbons represented have one or more double bonds or triple bonds and can be linear or cyclic. In addition, there are cases where structural isomers or stereoisomers (trans (E-form) and cis (Z-form)) exist in the C x F y represented unsaturated perfluorocarbons. In the present invention, they can be used in the form of any isomer or a mixture of both. As C2F4, tetrafluoroethylene can be cited. As C3F6, hexafluoropropene can be cited. As C4F6, hexafluoro-1,3-butadiene, hexafluoro-2-butyne, hexafluorocyclobutene can be cited. As C4F8, octafluoro-2-butene, octafluoro-1-butene, octafluoroisobutene can be cited. As C5F8, octafluoro-1,4-pentadiene, octafluorocyclopentene can be cited. As C5F 10 , decafluoro-1-pentene can be cited.

[0043] As C3H2F4, any one of 2,3,3,3-tetrafluoropropene (HFO-1234yf), trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), and cis-1,3,3,3-tetrafluoropropene (HFO-1234ze(Z)) can also be used. It is particularly preferred to use the trans form and / or the cis form of 1,3,3,3-tetrafluoropropene.

[0044] C x F y The unsaturated perfluorocarbon represented by has an unsaturated bond in the molecule, so it polymerizes in the plasma to form a high polymer, and accumulates on the side walls of the through holes to form a protective film. Therefore, the isotropic etching of SiN by only C3H2F4 can be suppressed.

[0045] In terms of obtaining a sufficient etching rate, the concentration of C3H2F4 is preferably 1% by volume or more, particularly preferably 5% by volume or more, relative to the total flow rate of the dry etchant containing the following oxidizing gas, inert gas, etc. in C3H2F4 and C x F y Also included in is that the total concentration of the dry etchant containing the following oxidizing gas, inert gas, etc. is preferably 5% by volume or more. In addition, the total concentration of C3H2F4 and C x F y in the dry etchant is preferably 5% by volume or more of the total flow rate. On the other hand, if the total concentration of C3H2F4 and C x F y exceeds 50% by volume of the total flow rate, the concentration of the oxidizing gas at a sufficient ratio cannot be ensured. Although it contains a large amount of expensive fluorinated unsaturated hydrocarbons, the etching rate does not increase instead, and it is not good in terms of cost-effectiveness.

[0046] In addition, the mixing ratio of the unsaturated perfluorocarbon represented by C3H2F4 and C x F y is preferably 1:0.1 to 10, more preferably 1:0.2 to 1.0, and particularly preferably 1:0.4 to 0.7 by volume ratio. If the unsaturated perfluorocarbon represented by C x F y is excessive, the anisotropic etching rate of the SiN layer in the vertical direction may also be significantly reduced, and the required etching shape may not be obtained.

[0047] C x F y The unsaturated perfluorocarbon represented by polymerizes in the plasma to form a high polymer due to having a double bond or a triple bond in the molecule, and a protective film is also formed on a mask such as a resist. Thus, a sufficient etching selectivity can also be obtained for the resist. On the other hand, in the case of using a saturated perfluorocarbon, although the etching rate of SiO x relative to the etching rate of SiN (SiN / SiO x ratio) can be slightly controlled, the degree is not sufficient. In addition, the etching selectivity with the mask cannot be obtained, and it is not suitable as an etching gas for ultra-high aspect ratio etching with an aspect ratio exceeding 20.

[0048] In the present invention, since the etching rates of the SiN layer and the SiO x layer can be arbitrarily controlled, the SiN layer and the SiO can be processed in one stepx Etch the laminated film of the layer. In addition, since the etching rates are the same, the unevenness on the walls (inner surfaces) of the holes formed in the laminated film is small, and holes with uniform upper and lower hole diameters can be formed in the laminated film.

[0049] In addition, an oxidizing gas is added to the dry etchant. As the oxidizing gas, O2, O3, CO, CO2, COCl2, COF2, NO2, etc. can be used. In particular, in terms of ease of acquisition and operation, oxygen is preferably used. The addition amount of the oxidizing gas is preferably 1 vol% to 50 vol% of the entire dry etchant, more preferably 2 vol% to 30 vol%, and particularly preferably 5 vol% to 10 vol%.

[0050] In addition, in order to reduce costs and improve the safety of operation, an inert gas is preferably included in the dry etchant. As the inert gas, noble gases such as argon, helium, neon, krypton, and xenon or nitrogen can be used. In terms of achieving ease of acquisition and expecting an ion-assisted effect, argon is particularly preferred. In addition, the dry etchant may also consist only of unsaturated perfluorocarbons represented by C3H2F4, C x F y an oxidizing gas, and an inert gas.

[0051] Known gases can also be added to the dry etchant. As the added gas, C l H m F n (where l is an integer from 1 to 5, m and n are positive integers, and m + n = 21 or 21 + 2) saturated fluorocarbons, hydrocarbon gases, halogen-containing gases, reducing gases, etc. can be listed. As the C l H m F n saturated fluorocarbons represented, CHF3, CH2F2, CH3F, C2H2F4, C2HF5, C3HF7, C3H2F6, C3H3F5, C3H4F4, C3H5F3, C4HF9, etc. can be listed. As the hydrocarbon gases, CH4, C2H2, C2H4, C2H6, C3H4, C3H6, C3H8, etc. can be listed. As the halogen-containing gases, F2, Cl2, Br2, I2, YF n (where Y = Cl, Br or I, and n is an integer from 1 to 7), NF3, HF, HCl, HBr, HI, etc. can be listed. As the reducing gases, H2, NH3, NO, etc. can be listed. In addition, the dry etchant may also consist only of unsaturated perfluorocarbons represented by C3H2F4, C x F y an oxidizing gas, an inert gas, and the added gas.

[0052] In order to perform etching with high linearity in the vertical direction of the layer, the generated bias voltage is required to be 500 V or more, preferably 1000 V or more. The higher the bias voltage, the more the side etching can be reduced. On the other hand, if the bias voltage exceeds 10000 V, the damage to the substrate becomes large, so it is not good.

[0053] Regarding the gas components contained in the etching gas, they can be independently introduced into the chamber respectively, or they can also be adjusted to a mixed gas in advance and then introduced into the chamber. The total flow rate of the dry etchant introduced into the reaction chamber can be appropriately selected according to the volume of the reaction chamber and the exhaust capacity of the exhaust part, taking into account the concentration conditions and pressure conditions.

[0054] In order to obtain a stable plasma and to suppress side etching to improve the linearity of ions, the pressure during etching is preferably 10 Pa or less, more preferably 5 Pa or less, and particularly preferably 1 Pa or less. On the other hand, if the pressure in the chamber is too low, the number of ionized ions becomes small and a sufficient plasma density cannot be obtained, so it is preferably 0.05 Pa or more.

[0055] In addition, the substrate temperature during etching is preferably 50 °C or less. In particular, for anisotropic etching, it is ideally set to 20 °C or less. At a high temperature exceeding 50 °C, the amount of the protective film mainly composed of fluorocarbon radicals formed on the sidewalls decreases, the tendency to etch isotropically is enhanced, and the required processing accuracy cannot be obtained. In addition, there is a case where a mask material such as a resist is significantly etched.

[0056] If the efficiency of the device manufacturing process is considered, the etching time is preferably within 30 minutes. Here, the etching time refers to the time when plasma is generated in the chamber and the dry etchant reacts with the specimen.

[0057] The number of layers in the laminated film or the depth of the formed through holes is not particularly limited. In terms of obtaining the integrated effect of lamination, the total number of SiN layers and SiO x layers is preferably 6 layers or more, and the depth of the through holes is 0.5 μm or more.

[0058] In addition, the etching method using the dry etchant of the present invention can be carried out without being limited to various etching methods such as capacitively coupled plasma (CCP) etching, reactive ion etching (RIE), inductively coupled plasma (ICP) etching, electron cyclotron resonance (ECR) plasma etching, and microwave etching.

[0059] In addition, when forming through holes in a laminated film containing SiN layers and SiO x layers, it is not necessary to use C3H2F4 and C contained in the dry etchant during the etching step x F yThe composition is fixed at a certain composition ratio, or it can be changed periodically or intermittently during the etching step. If the amount of C x F y is reduced, SiN can be etched at high speed. If the amount of C x F y is increased, although the SiN etching in the horizontal direction can be suppressed, the SiN etching rate will decrease. Therefore, by appropriately changing the amount of C x F y during the etching step, it is possible to balance the shortening of the through-hole formation time and the suppression of the SiN etching in the horizontal direction. For example, in the latter half of the through-hole formation, since the influence on the horizontal etching of the SiN layer forming the side wall of the upper part of the through-hole is large, the amount of unsaturated perfluorocarbon contained in the dry etchant can be increased compared to the amount in the first half of the through-hole formation. In addition, when etching the SiN layer of the laminated film, in order to increase the etching rate, the amount of unsaturated perfluorocarbon contained in the dry etchant can be reduced. When etching the SiO x layer, in order to suppress the horizontal etching of the SiN layer, the amount of unsaturated perfluorocarbon contained in the dry etchant can be increased.

[0060] In addition, when forming a through-hole, a dry etching step using a dry etchant that does not contain C x F y may be included, that is, a step of etching using a dry etchant containing C3H2F4 and an oxidizing gas and substantially not containing C x F y . In addition, the content of C x F y contained in C3H2F4 for etching as an impurity is usually 0.1% by volume or less. Therefore, the content of C x F y in the dry etchant containing C3H2F4 and an oxidizing gas and substantially not containing C x F y is usually 0.1% by volume or less.

[0061] For example, as an example, consider that in the first half of the through-hole formation, that is, when etching to about half of the laminated film (for example, 1 / 2 to 5 / 8 of the thickness of the laminated film), a first dry etching step using a first dry etchant containing C3H2F4 and an oxidizing gas and substantially not containing C x F y is performed. In the latter half of the through-hole formation, that is, after cutting about half of the laminated film, a step of using a dry etchant containing C3H2F4, an oxidizing gas, and C x F yThe second dry etching step of the second dry etchant. According to this method, horizontal SiN etching is not likely to occur. In the stage of starting to cut through the through-hole, high-speed etching of SiN can be performed through the first etching step. In the stage of finishing cutting through the through-hole where horizontal SiN etching becomes a problem, through the second dry etching step, C can be added to the dry etchant x F y to suppress horizontal SiN etching and etch the stacked film. That is, horizontal SiN etching can be prevented, and the time required to form through-holes can be shortened.

[0062] In addition, as another example, consider that when etching the SiN layer of the stacked film, apply the first etching step of etching without adding C x F y and perform the first etching step. When etching the SiO x layer of the stacked film, apply the etching method of the present invention, that is, the second etching step. According to this method, when etching the SiO x layer, the second etching step capable of suppressing lateral etching of the SiN layer can be applied. When etching the SiN layer, the first etching step of etching SiN with a dry etchant that is fast in SiN etching speed and does not add C x F y can be applied.

[0063] In addition, in this method, the dry etchant supplied must be changed according to the number of stacked layers of the SiN layer and the SiO x layer. However, as long as the supply of C x F y is switched, the dry etchant can be changed. Therefore, there is no need for a large amount of operation in switching the etching method for each layer, and the steps are not so complicated.

[0064] On the other hand, in Non-Patent Document 3, since halogen gas is used when etching the Si layer and fluorocarbon gas is used when etching the SiO2 layer, chamber evacuation must be performed when switching the etching of each layer, and a large amount of operation is required. The steps are complicated and time-consuming.

[0065] The etching method of the present invention can perform the following etching, that is, the etching rate of SiO x can be arbitrarily controlled to be 0.90 or more and less than 1.5 relative to the etching rate of SiN (SiN / SiO x ratio), and it also has high selectivity for the mask. Therefore, in the process of manufacturing a three-dimensional NAND flash memory, the etching method of the present invention can be used for the step of forming through-holes with an aspect ratio exceeding 20 in the alternately stacked film of SiN and SiO x .

[0066] According to the etching method of the present invention, in order to remove the reactive products or masks generated by C x etc. accumulated on the side walls of the through holes after forming through holes in the stacked film including the SiN layer and the SiO x F y layer, an ashing step of ashing these substances using plasma generated from a processing gas containing oxygen can also be performed.

[0067] [Examples]

[0068] Hereinafter, examples and comparative examples of the present invention are listed simultaneously, but the present invention is not limited to the following examples.

[0069] [Example 1]

[0070] (Etching Step)

[0071] Figure 3 is a schematic diagram of the reaction apparatus 10 used in the examples and comparative examples. Inside the chamber 11, a lower electrode 14, an upper electrode 15, and a pressure gauge 12 are provided, which have the function of holding the specimen 18 and also function as a stage. In addition, a gas inlet 16 is connected to the upper part of the chamber 11. The pressure inside the chamber 11 can be adjusted, and the dry etchant can be excited by a high-frequency power supply (13.56 MHz) 13. Thus, the excited dry etchant can be brought into contact with the specimen 18 provided on the lower electrode 14, and the specimen 18 can be etched. It is configured as follows: If high-frequency power is applied from the high-frequency power supply 13 in a state where the dry etchant is introduced, a DC voltage called a bias voltage can be generated between the upper electrode 15 and the lower electrode 14 due to the difference in the moving speeds of ions and electrons in the plasma. The gas inside the chamber 11 is discharged through the gas discharge pipeline 17.

[0072] As the specimen 18, a silicon wafer A having a SiN layer and a silicon wafer B having a SiO2 layer are placed on the stage. The SiN layer or the SiO2 layer is formed by CVD (chemical vapor deposition) method.

[0073] Here, as the etchant, C3H2F4 (HFO-1234ze(E)), C3F6, O2, and Ar are mixed at 10 vol%, 1 vol%, 6 vol%, and 83 vol% respectively with respect to the total flow rate, and the total is set to 100 sccm, and they are made to flow, and high-frequency power of 400 W is applied to plasmaize the etchant, thereby performing etching. In addition, the bias voltage is 500 V.

[0074] The etching rate is obtained from the thickness change of the SiN layer of the silicon wafer A and the SiO2 layer of the silicon wafer B before and after etching.

[0075] [Example 2]

[0076] As an etchant, C3H2F4 (HFO-1234ze(E)), C3F6 (hexafluoropropene), O2 and Ar were mixed at 10 vol%, 3 vol%, 6 vol%, and 81 vol% with respect to the total flow rate, respectively. Except for this, etching was performed under the same conditions as in Example 1.

[0077] [Example 3]

[0078] As an etchant, C3H2F4 (HFO-1234ze(E)), C3F6, O2 and Ar were mixed at 10 vol%, 5 vol%, 6 vol%, and 79 vol% with respect to the total flow rate, respectively. Except for this, etching was performed under the same conditions as in Example 1.

[0079] [Example 4]

[0080] As an etchant, C3H2F4 (HFO-1234ze(E)), c-C5F8 (octafluorocyclopentene), O2 and Ar were mixed at 10 vol%, 1 vol%, 6 vol%, and 83 vol% with respect to the total flow rate, respectively. Except for this, etching was performed under the same conditions as in Example 1.

[0081] [Example 5]

[0082] As an etchant, C3H2F4 (HFO-1234ze(E)), c-C5F8, O2 and Ar were mixed at 10 vol%, 3 vol%, 9 vol%, and 78 vol% with respect to the total flow rate, respectively. Except for this, etching was performed under the same conditions as in Example 1.

[0083] [Example 6]

[0084] As an etchant, C3H2F4 (HFO-1234ze(E)), C4F6 (hexafluoro-1,3-butadiene), O2 and Ar were mixed at 10 vol%, 1 vol%, 6 vol%, and 83 vol% with respect to the total flow rate, respectively. Except for this, etching was performed under the same conditions as in Example 1.

[0085] [Example 7]

[0086] As an etchant, C3H2F4 (HFO-1234ze(E)), C4F6, O2 and Ar were mixed at 10 vol%, 3 vol%, 9 vol%, and 78 vol% with respect to the total flow rate, respectively. Except for this, etching was performed under the same conditions as in Example 1.

[0087] [Example 8]

[0088] As an etchant, C3H2F4 (HFO-1234ze(E)), C4F6, O2, and Ar were mixed at 5 vol%, 10 vol%, 6 vol%, and 79 vol% relative to the total flow rate, respectively. Other than that, etching was performed under the same conditions as in Example 1.

[0089] [Comparative Example 1]

[0090] As an etchant, C3H2F4 (HFO-1234ze(E)), O2, and Ar were mixed at 10 vol%, 6 vol%, and 84 vol% relative to the total flow rate, respectively, and unsaturated perfluorocarbon was not added. Other than that, etching was performed under the same conditions as in Example 1.

[0091] [Comparative Example 2]

[0092] As an etchant, C3H2F4 (HFO-1234ze(E)), c-C4F8 (octafluorocyclobutane), O2, and Ar were mixed at 10 vol%, 3 vol%, 9 vol%, and 78 vol% relative to the total flow rate, respectively. Other than that, etching was performed under the same conditions as in Example 1.

[0093] [Comparative Example 3]

[0094] As an etchant, C3H2F4 (HFO-1234ze(E)), C2F6 (hexafluoroethane), O2, and Ar were mixed at 10 vol%, 3 vol%, 9 vol%, and 78 vol% relative to the total flow rate, respectively. Other than that, etching was performed under the same conditions as in Example 1.

[0095] [Comparative Example 4]

[0096] As an etchant, C3H2F4 (HFO-1234ze(E)), C3F8 (octafluoropropane), O2, and Ar were mixed at 10 vol%, 3 vol%, 9 vol%, and 78 vol% relative to the total flow rate, respectively. Other than that, etching was performed under the same conditions as in Example 1.

[0097] [Comparative Example 5]

[0098] As an etchant, C3H2F4 (HFO-1234ze(E)), C3F6, O2, and Ar were mixed at 1 vol%, 11 vol%, 6 vol%, and 82 vol% relative to the total flow rate, respectively. Other than that, etching was performed under the same conditions as in Example 1.

[0099] [Comparative Example 6]

[0100] As an etchant, C3F6, O2, and Ar were mixed at 10 vol%, 6 vol%, and 84 vol% with respect to the total flow rate, respectively, and etching was performed under the same conditions as in Example 1 except for this.

[0101] [Comparative Example 7]

[0102] As an etchant, C3H2F4 (HFO-1234ze(E)), TFPy (3,3,3-trifluoropropyne), O2, and Ar were mixed at 10 vol%, 3 vol%, 9 vol%, and 78 vol% with respect to the total flow rate, respectively, and etching was performed under the same conditions as in Example 1 except for this.

[0103] The results of each example and comparative example are shown in Table 1. The etching rate ratio in Table 1 is the ratio of the etching rate of SiO x to the etching rate of SiN (SiN / SiO x ratio), and the etching selectivity is the ratio of the etching rate of the resist to the etching rate of SiO x (SiO x / resist ratio).

[0104] [Table 1]

[0105]

[0106] In each example using a dry etchant containing at least C3H2F4 and an unsaturated perfluorocarbon represented by C x F y and having a mixing ratio of 1,3,3,3-tetrafluoropropene to the unsaturated perfluorocarbon in the range of 1:0.1 to 10 by volume ratio, the etching rate ratio of SiN to SiO x is 0.90 or more and less than 1.5, and the selectivity with respect to the resist is also equal to or higher than that in the case of not adding. By this dry etching method, over-etching of the SiN layer can be suppressed and anisotropic etching of a laminated film containing SiO x and SiN can be performed. In addition, as is clearly known from Examples 6 to 8 and the like, by adjusting the ratio of C3H2F4 to the unsaturated perfluorocarbon, the etching rate ratio of SiN to SiO x can be controlled.

[0107] On the other hand, in Comparative Example 1, since it does not contain the unsaturated perfluorocarbon represented by C x F y , the SiN etching rate is too high, and the ratio of the SiN etching rate to the SiO x etching rate is 1.63. In addition, in Comparative Examples 2, 3, and 4, a saturated perfluorocarbon having no double bond was used as an additive gas. As a result, the SiN etching rate and the SiO xThe ratio of the etching rate is 1.5 or more, and the selectivity with respect to the resist also deteriorates compared to the case where no addition is made. In the case of such saturated perfluorocarbons, it is considered that the ratio of CF3 radicals contained in the plasma becomes relatively large, and the ratio of radicals such as CF2 or C2F4 having high polymerizability becomes relatively small. Therefore, it is considered that the adhesion of the polymer film to SiN or the resist becomes less, and the protective effect on SiN and the resist is not effectively exhibited. Therefore, if Comparative Examples 1 to 4 are applied to the laminated film of SiN and SiO x etching in the horizontal direction of the SiN layer will proceed, and the structure of the laminated film may collapse. In addition, in Comparative Examples 2 to 4, since the etching selectivity ratio with respect to the resist deteriorates, it is difficult to form through-holes having an aspect ratio of 20 or more.

[0108] Figure 4 (a) and (b) show SiN / SiO of Comparative Example 1 without added gas and Examples 2, 5, 7 with different gas types but an added gas amount of 3 vol%, and Comparative Examples 2, 3, 4, 7 x graphs of the etching rate ratio and the etching selectivity ratio (SiO x / resist). As Figure 4 (a) shows, when C3F6, C5F8, or C4F6, which is an unsaturated perfluorocarbon having a double bond, is added, the SiN / SiO x etching rate ratio is successfully reduced compared to the case where no addition is made. However, when c-C4F8, C2F6, or C3F8, which is a saturated perfluorocarbon having no double bond, is added, or when TFPy having a triple bond but also having hydrogen is added, it is roughly the same as the case where no addition is made. In addition, as Figure 4 (b) shows, when C3F6 or C5F8, which is an unsaturated perfluorocarbon having a double bond, is added, the etching selectivity ratio (SiO x / resist) is significantly improved compared to the case where no addition is made. A slight improvement is also found when C4F6 is added. However, when c-C4F8, C2F6, or C3F8, which is a saturated perfluorocarbon having no double bond, is added, the selectivity ratio decreases instead compared to the case where no addition is made. When TFPy having a triple bond but also having hydrogen is added, the selectivity ratio is greatly improved.

[0109] As described above, the adhesion of a protective film of saturated perfluorocarbon without unsaturated bonds to SiN or a resist is poor, and the protective effect is not effectively exhibited. Fluorocarbon with a double bond or a triple bond polymerizes in a plasma to form a protective film, which can suppress the etching of SiN or a resist. However, fluorocarbon containing hydrogen (such as C3F4H2 or TFPy, which is the main etching gas) generates more active substances for SiN etching, so the SiN etching rate cannot be suppressed. The additive gas that can further improve the resist selectivity ratio and suppress the SiN etching rate is unsaturated perfluorocarbon with an unsaturated bond and no hydrogen.

[0110] In Comparative Example 5, an unsaturated perfluorocarbon represented by adding C at a ratio exceeding 10 with respect to C3H2F4 x F y was used, and the SiN etching rate was too low. The ratio of the SiN etching rate to the SiO x etching rate became 0.89, and the selectivity with respect to the resist also deteriorated compared with the case where it was not added.

[0111] In Comparative Example 6, since only C3F6, that is, unsaturated perfluorocarbon, was used, the SiN etching rate was slow, and the ratio of the SiN etching rate to the SiO x etching rate became 0.85. Therefore, it is considered that even if Comparative Example 6 is applied to a laminated film of a SiN layer and a SiO x layer, deposits from the gas will accumulate on the SiN layer, and via holes cannot be formed.

[0112] In Comparative Example 7, TFPy containing a hydrogen atom and having a triple bond was added, and the etching selectivity ratio of SiO x / resist was greatly improved, but the SiN / SiO x etching rate ratio did not change much compared with Comparative Example 1. That is, it is considered that the protective film derived from TFPy is mainly formed on the resist and hardly formed on the SiN layer.

[0113] [Industrial Applicability]

[0114] The present invention is effective for forming wiring on elements such as three-dimensionally integrated NAND flash memories in a semiconductor manufacturing process.

[0115] [Description of Reference Numerals]

[0116] 1 SiN layer

[0117] 2 SiO x layer

[0118] 3 Mask

[0119] 4 Substrate

[0120] 5 Via hole

[0121] 10 Reaction device

[0122] 11 Chamber

[0123] 12 Manometer

[0124] 13 High-frequency power supply

[0125] 14 Lower electrode

[0126] 15 Upper electrode

[0127] 16 Gas inlet

[0128] 17 Exhaust pipeline

[0129] 18 Specimen

Claims

1. A dry etching method, characterized in that: It is a method of forming a through-hole in the vertical direction in the laminated film by etching a laminated film of a silicon oxide layer and a silicon nitride layer formed on a substrate, with a dry etchant being made into plasma and a bias voltage of 500 V or more being applied through a mask having a specific opening pattern formed on the laminated film, and The dry etchant contains at least C3H2F4, C x F y represented unsaturated perfluorocarbon and oxidizing gas, where x is an integer from 2 to 5, y = 2, 4, 6, 8 or 10, and y ≤ 2x, the volume of the unsaturated perfluorocarbon contained in the dry etchant is in the range of 0.1 to 10 times the volume of C3H2F4 contained in the dry etchant, and To make the composition ratio of C3H2F4 and C x F y change periodically or intermittently, so as to balance the shortening of the formation time of the through holes and the suppression of SiN etching in the horizontal direction.

2. The dry etching method according to claim 1, wherein: the unsaturated perfluorocarbon is at least one selected from the group consisting of C3F6, C4F6, C4F8, and C5F8.

3. The dry etching method according to claim 1, characterized in that: The total concentration of the unsaturated perfluorocarbon and C3H2F4 in the dry etchant is 5 vol% or more.

4. The dry etching method according to claim 1, characterized in that: The oxidizing gas is at least one selected from the group consisting of O2, O3, CO, CO2, COCl2, COF2, and NO2.

5. The dry etching method according to claim 1, wherein: The dry etchant further contains an inert gas, and the inert gas is at least one selected from the group consisting of He, Ne, Ar, Kr, Xe, and N2.

6. The dry etching method according to claim 5, characterized in that: The dry etchant contains only C3H2F4, the unsaturated perfluorocarbon, the oxidizing gas, and the inert gas.

7. The dry etching method according to claim 1, characterized in that: C3H2F4 is 1,3,3,3-tetrafluoropropene.

8. The dry etching method according to claim 1, wherein: The mask contains amorphous carbon.

9. The dry etching method according to claim 1, characterized in that: The depth of the through-hole is 0.5 μm or more.

10. The dry etching method according to claim 1, wherein: The aspect ratio obtained by dividing the depth of the through-hole by the width of the opening pattern is 20 or more.

11. The dry etching method according to claim 1, characterized in that: The laminated film is an alternating laminated film of 32 layers or more.

12. The dry etching method according to claim 1, characterized in that: The value of the etching rate of silicon nitride divided by the etching rate of silicon oxide, the SiN / SiOx etching rate ratio, is 0.9 to 1.

5.

13. The dry etching method according to claim 1, characterized in that: The SiOx / resist etching rate ratio obtained by dividing the etching rate of silicon oxide by the etching rate of the resist is 2.5 or more.

14. The dry etching method according to claim 5, wherein: the C3H2F4 is 1,3,3,3-tetrafluoropropene, the unsaturated perfluorocarbon is at least one selected from the group consisting of C3F6, C4F6, C4F8, and C5F8, the inert gas is Ar, the oxidizing gas is O2.

15. The dry etching method according to claim 14, wherein: The dry etchant contains only C3H2F4, the unsaturated perfluorocarbon, the oxidizing gas, and the inert gas.

16. The dry etching method according to claim 1, characterized in that: The laminated film is an alternating laminated film of the silicon oxide layer and the silicon nitride layer, and the total number of layers of the silicon oxide layer and the silicon nitride layer is 6 layers or more.

17. The dry etching method according to claim 1, wherein: The unsaturated perfluorocarbon is C3F6.

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